214 CHEMICAL AGENTS AND GROWTH 



that induced by light. None of them has been capable of substituting 

 for a light treatment in the bean hook test, with the exception of the 

 cobalt ion. Cobalt has the ability to cause the hook to open about 60° 

 at lO^M; this effect is additive to a light stimulus and would indicate 

 that two different sites are affected. Cobalt is the only stimulus we have 

 tested which can stimulate, even partially, the response produced by 

 light in the hypocotyl hook of bean. 



There is a definite interaction between infiltrated FMN and blue 

 irradiance on the opening of the hypocotyl hook. However, it does not 

 appear to have any relationship to added lAA. Since FMN can absorb 

 the blue radiation and fluorescence in the yellow-green portion of the 

 spectrum, one possible explanation for the added response induced by 

 the presence of FMN is that the yellow fluorescent energy emitted by 

 FMN is reabsorbed by the photomorphogenic pigment. Measurements 

 of the fluorescent energy indicate that the emitted energy is sufficiently 

 high to produce a hook response, and experiments using the fluorescent 

 emission from FMN solutions do cause a considerable hook opening. 



SUMMARY 



1. The opening of the excised hypocotyl hook of bean is brought 

 about by the stimulation of cell elongation on the inside (concave) of 

 the hook and not by cell division, since no mitotic stages have been 

 detected in any prepared slides. The elongation is proportional to the 

 incident energy. 



2. lAA, gibberellin, and kinetin can affect the growth response of 

 the hypocotyl hook in a negative manner, either in the dark or in the 

 presence of red radiant energy. There is no evidence to indicate any 

 interaction between red radiant energy and the added substances. 



3. Cobalt at 10 W is the only additive found that can induce a 

 hook opening in the dark to an appreciable degree. This effect of cobalt 

 is additive to the red light response and the magnitudes of the re- 

 sponses are not comparable. It appears to cause hook opening via some 

 other pathway than the photoreaction. The maximum response induced 

 by the optimum concentration (10 "M) of cobalt is only about 60°, 

 whereas red radiant energy can produce about three times this re- 

 sponse. 



4. Hooks infiltrated with 10~W FMN interact with blue radiant 



